I've been following the work of Elton Roberts since I first found out about him through the Cultivation forum last December. That introduction was quite revealing when I discovered his CSSJ article on cacti and alkalinity. Then recently I started hearing about Elton's fertilizer regimen, and I emailed him to ask for some more in-depth information. He was kind enough to oblige my request, and it turns out that's where the real discovery was. This has completely changed my approach to fertilizing cacti and succulents, and I'd like to pass along what I've been finding for anyone who may get some use out of it. Before I continue, I should mention that when all plants are watered using hard water, they will suffer the effects sooner or later. By neutralizing the Calcium bicarbonate in hard water through acidification, plants are able to absorb the moisture and nutrients they need through their roots. I'll discuss fertilizers before we look at acidification, but you should know that the two need to go hand-in-hand. If you don't address the pH in your water, then all the fertilizer in the world won't do any good for your c&s.

Fertilizers

I've been reading and re-reading Elton's article Ammonium Nitrogen and Acidic Water for Xerophytic Plant Growth from the July 2010 issue of the Cactus and Succulent Journal, and it becomes increasingly apparent that all three sources of Nitrogen are not equal when it comes to maintaining optimum health for c&s over the long term. I have two versions of his article for you here. The first one includes photos showing examples of some cacti before and after using fertilizer supplemented with Ammonium sulfate:

I highly recommend that you read Elton's article in more detail for yourself, but I can give you a "Cliff Notes" summary to guide you through the rest of this section. For starters, please note that Ammonium Nitrogen packs a lot more nutrient value than either Nitrate or Urea for c&s. Now here's the problem -- Ammoniacal N comprises only part of the total N in ferts. Since the "big three" major nutrients are N, Phosphorus (P), and Potassium (K), you'll need to supplement your fert with Ammonium sulfate to achieve the proper NPK balance.

There are two things we need to be aware of. First, when c&s are kept in pots, they'll need a steady nutrient supply. Therefore it's better to use low fert levels with each watering, instead of "juicing up" the plants once in awhile as they get nutrient-deprived the rest of the time. Second, the amount of Ammonium N depends on the potting medium. Since humus removes N from the soil, a high-humus mix will require more Ammonium N than a mix with little or no humus. I'm using a pumice/decomposed granite mix myself, so there's not even a hint of humus in it. Since I don't have any experience with a mix that uses humus, I'll have to try and extrapolate from Elton's article for you the best I can.

Okay, we're really getting into it now, aren't we? If you don't mind doing some math, you'll find that learning how to speak in parts-per-million will really help you to determine the amount of NPK being delivered to your c&s through regular watering. (If you're math-challenged, you can skip down to the end of this section, and I'll give you a simple recommendation.) Let's begin with Elton's regimen for high-humus soils. His fert is Plantex 20-20-20 diluted at 4 tbsp. supplemented with 8 tbsp. of Ammonium sulfate per 30 gallons of water. When I run the numbers, we see that the Plantex has 100 ppm each for N, P, and K. However, only 20 ppm is Ammonium N, and in a high-humus soil it might as well not even be there. (The plants are still getting their P and K, though.) When we supplement the Plantex with Ammonium sulfate, we'll get 219 ppm of that for a total of 239 ppm Ammonium N. What we're doing is basically a combination of two different ferts to get our c&s the major nutrients they need. The same goes with mineral soils, although we need a different set of numbers here. For a mineral mix, the dilution rate will be 2 tbsp. Plantex and 2 tbsp. Ammonium sulfate per 30 gallons of water. That gives us 52 ppm each of NPK from the Plantex, although only 10 ppm will come as Ammonium N. The Ammonium sulfate makes up 55 ppm, giving us a total of 65 ppm Ammonium N.

The difference between high-humus and mineral soils is both apparent and rather dramatic in terms of their impact on nutrient delivery. With that said, Elton's article doesn't provide any guidelines on what would constitute a high-humus mix, although this may have to be left up to the knowledge and experience of the individual grower. For those who are using mixes with only a small amount of humus, it stands to reason that fert dilutions should be adjusted downward toward the lower end of the NPK scale, but how low should it be? Once again this must be up to the grower. What we can say with certainty is that under-fertilizing is preferable to over-fertilizing, especially over the long term.

The ppm values for Ammonium N, P, and K I'm discussing here should be good benchmarks for any fert one would like to use when supplemented with Ammonium sulfate. However, the proper dilution rates need to be calculated. (Knowing the amount of Ammonium N in your fert is essential to determining the amount of Ammonium sulfate required.) If you feel so inclined, I'm showing my work at the end of this post to give you the basic calculations you'll need. That work also includes calculations for the Dyna-Gro All Pro 7-7-7 and Ammonium sulfate I'm using in my pumice/DG mix. Last year I gave my cacti a controlled-release fert which I now know was pretty much useless, so I'm having to make up for lost time as they're coming out of their nutrient deficiency. To avoid the risk of over-fertilizing, I'll cut my Dyna-Gro and Ammonium sulfate by half, which in turn will bring the ppm values pretty much in line with what Elton recommends for mineral soils. This is a good example of how adjustments can be made when observant growers use some common sense.

I know math exercises may not be something you'd want to deal with, so if you follow the fert "recipes" in Elton's article, that'll give you the right dilutions for whatever mix you're using.

Acidification

As I briefly mentioned earlier, Calcium bicarbonate in tap/well water slowly robs plants of their ability to take up moisture and nutrients through the roots. This is precisely why acidification is necessary in order for plants to thrive when your only source comes from hard water. Vinegar and citric acid are both very safe for home use, although not the most practical or cost-effective for large collections and nurseries. In those cases, Sulfuric and Phosphoric acids are better, although they must be treated very carefully, and should not be used until you know how to properly handle them. I'll direct you to Elton's article on cacti and alkalinity for more information here:

Based on advice from expert growers, we know that a pH of 5.0 - 5.5 is optimal for the health of c&s. Ferts themselves will lower the pH of water, but not enough to do the job. After diluting your fert, you'll need the right amount of acid to bring the pH down into the 5.0 - 5.5 range. Some people try to "guesstimate", but in my opinion it is a poor substitute for knowing the actual pH values in your watering/fert solution. If you can determine those values, the idea is to start with a small amount of acid, check the pH, then continue adding small amounts until you reach the desired final pH. Once you've done this a few times, you should know about how much acid you'll need. However, the pH of the water coming out of your tap can fluctuate, so checking the pH right before each watering is advisable to avoid inadvertently straying from the 5.0 - 5.5 range. If you find that the pH of your watering/fert solution is below 5, throw it away and start again.

Inexpensive colorimetric indicator kits can be found at any hydroponic store, but they tend to be highly inaccurate. I've seen this for myself, and before I started using my water/fert/vinegar regimen on my cacti, I decided to buy a pH meter for the sake of both accuracy and precision. It is understandable for one to feel intimidated by the idea of getting a pH meter, but A. good ones aren't expensive and they're easy to replace when they stop working, and B. pH meters are easy to use if you know how to follow basic instructions. I purchased a Milwaukee Instruments PH600 meter for $21.95 through Amazon, and it has proven to be not only simple, but also rugged and reliable, so I'd definitely recommend it. Here's the link:

Hard water is the primary reason for citing the use of acidification, but it should by no means be the only one. For example, what about distilled water? Since it is supposed to be free of minerals, then it should theoretically have a neutral (7.0) pH. Well, there's a myth I can bust for you -- I recently bought a gallon of distilled water from my local grocery store. I decided to test it with my pH meter, and guess what. The pH was 7.9! How that could be I don't know, but I'd have to acidify it just as much as anything coming out of my tap. (Moral of the story, don't assume anything.) You won't have that with rainwater, since it will be more or less pH-neutral. However, even rainwater with a dilute fert may not give you the desired 5.0 - 5.5 pH range, so you'll probably still need to acidify a little bit. If you're already using rainwater, you may be saying "rainwater + fert = 6.0 pH. That's good enough." Maybe not. Thunderstorm activity fixes Nitrogen through Nitric acid in rainwater. Anyone who has spent time in the desert will know that rain almost invariably comes with thunderstorms. Rain + Nitric acid from lightning = low pH, and the rainwater pH can go as low as about 3.7. (Read Elton's article on cacti and alkalinity, and pay close attention to what he discusses regarding cacti in limestone-rich desert soils. I think you'll find it rather interesting.) In the absence of local thunderstorm activity, acidifying your rainwater/fert solution is useful if it needs to bring the pH down to the 5.0 - 5.5 range.

Conclusion

I recently corresponded with John Trager at the Huntington to ask him about his cultivation practices. John has been curator of the Desert Collections for many years, so those who know him (at least by reputation) understand that he is a wizard of a grower. Under the wisdom of "trust, but verify" I asked him about Elton's work, and he backs up what Elton has been telling us. Difficult to argue with this.

I've been incorporating Ammonium sulfate into my watering/fert regimen, although I just started doing it a couple of weeks ago. It's too soon for me to assess the results, but I have the whole summer ahead as I track the progress of my cacti. I'll be keeping my photo archive up to date while things move along, so if those results are good, I'll post before-and-after cactus pics in this thread. Until then, I'll leave you with a little story of what I hope will be a harbinger of good things to come.

Before I started my new collection in earnest last June, I went to my local Armstrong Garden Center just to see what they had in their c&s section. A lot of s, but not much c. (I did buy a Mammillaria spinossissima -- the "red-headed Irishman" has been an old favorite since I was a kid.) I also bought a Sempervivum tectorum ("hen with chicks") which caught my fancy. Then it didn't after I found all the cacti for my collection. I must admit that I neglected the poor thing, and the only water it got was some occasional rain. The Sempervivum was still alive, although barely, and I decided to try it on some of my new Dyna-Gro/Ammonium sulfate regimen. A few days later my "hen with chicks" was thriving. I could hardly believe it! Sorry I didn't take a "before" photo, but here's what the Sempervivum looks like today:

Sempervivum_tectorum07012012.JPG (223.29 KiB) Viewed 4209 times

If I've learned anything from Elton at all, then I'm off to a good start! And if it helps me, I hope it'll help you, too.

amanzed wrote:You put quite a bit of work into that post, thanks! I've been getting good results from acidification + ammoniacal nitrogen, too. I was keen on trying it after reading Elton Roberts' article in CSJ.

I've been following the basic ingredients but using guesstimates some of the time (even though my degrees are in math, sometimes I get lazy when it comes to measurement, buying pH meters, etc).

My pleasure, and thanks for your kind words there! I know it seems overly technical, but in practical use we don't need to be that precise -- I highly doubt that cacti would know the difference between, let's say 65 and 70 ppm. I'm more concerned with gross over- or under-fertilization, so doing the math on dilution rates and ppm is just basically to help people determine whether their ferts are fine or way out of whack. Sounds like you're doing well, although I wonder how many people out there have no idea if their ferts are doing any good at all.

Thanks again, guys! I have a follow-up which might be instructive. When I said I'm not using any humus for my cacti, that may not be entirely true.

Last June I got my cactus collection going with a bunch of plants I purchased from the California Cactus Center in Pasadena. I was also using their cactus mix, and apparently it's pretty much like SuperSoil. I don't know what the dirt component is, but the mix contains about 80% of that and about 20% fir bark (with just a touch of pumice or fine gravel added). Okay, not humus in the strict sense. But as I contemplated Elton's article again last night, it dawned on me that the CCC mix should be treated as a high-humus soil.

After I took a good, long look at my cultivation practices through the forum, I decided that the CCC mix wasn't doing anything for my cacti. At that point I was ready to ditch all the organic materials in March, and everything went into pumice/DG. Except for 2 plants. I have an Eriosyce senilis and a Melocactus matanzus, both of which don't like being disturbed (as in "don't repot unless you absolutely have to"). Such being the case, I've been keeping them in a 70% CCC mix/30% pumice medium since last year. The Eriosyce is doing well, but I'm not thrilled with the Melo. After winter shrinkage and nutrient deficiency, I thought that 3 months of regular watering and fertilizing would be enough to bring my matanzus back into its usual plumpness. Seems healthy enough -- good growth in the cephalium, and a few flowers are popping up here and there. But no plumping, and I can tell that the plant isn't getting enough Nitrogen by the color of its skin. I know what matanzuses (matanzi?) are supposed to look like. Taking a page from the Elton Roberts book, I'll put things to the test by doubling the amount of Ammonium sulfate going in with my Dyna-Gro 7-7-7. That'll give me 164 ppm Ammonium N, and 91 ppm each P and K, not far off from Elton's high-humus fert regimen. If my theory is correct, the total Ammonium N will be enough to overcome the Nitrogen that would be taken out of the CCC mix in a lower dilution. Proof in the pudding will be a plumper matanzus with dark green skin. And if this actually works, I'll be interested to see how long it takes.

By the way, after thinking about it a lot I decided to take a chance on repotting the Eriosyce and the Melo next year. The CCC mix doesn't have nearly enough pumice in it, and I'm sure their roots aren't doing as well as they should. One possibility would be to turn the ratio around and go with 70% pumice/30% CCC mix. Or I could try them as test plants with John Trager's 80/20 pumice/Forest Humus mix. In either case, the fert dilution should definitely be closer to what Elton recommends for mineral soils. I also wonder if supposedly "difficult" cacti get a bum rap because they're not receiving the right stuff like, well, the right fert and low-pH water. Hmmmm....

I'm pleased to report a rather dramatic "before and after" success story using Elton's fert/Ammonium sulfate regimen. One of the cacti I got for my collection last year was an Astrophytum capricorne var. senilis. The plant came to me with a serious case of red skin -- sunburn, obviously. I remember what sunburn used to do to some of my cacti back in the old days, and I was determined not to repeat that experience. Since my plant bench is under full sun (yes, just like the old days), I had the CCC special-order 40% shade cloth cut to fit for a frame I made over the bench. After I got all my plants under the shade cloth, a few sunburned items recovered almost immediately. I was hoping for the same with the Astro, but no -- it seemed like the sunburn would be permanent.

Fast forward to the end of March, when I started repotting my cacti in pumice/DG mix. Here's what the Astro looked like on April 29:

As you can see, the Astro was as red as ever, maybe even more so. After going through a long, dry winter no wonder it was stressed. Well, I figured that enough regular watering and fertilizing in the mineral mix might start to reverse the sunburn. However, keeping up my watering regimen with the Dyna-Gro 7-7-7 fert for 2 1/2 months produced very little greening of the skin. Then in mid-June I started supplementing the Dyna-Gro with Ammonium sulfate per Elton's recommended regimen. And the results over the last month and a half have been nothing short of amazing:

Who knows the last time the Astro was ever that healthy? But the substantial greening of its skin wasn't the only thing. Looking back to last year, it seemed that the Astro didn't grow at all over the summer. It did finally produce a bud (which took forever), and I saw a lovely flower at the end of October. This year a new bud started forming about 3 weeks ago (well ahead of schedule), and my guess is that I'll see it go into full flower in 2-3 weeks. If it gives me another flower after that, I'll be thrilled! And finally, I'm seeing slow, but steady new spines and other signs of growth on the apex of the plant itself. This is only 1 example of what Ammonium sulfate can do.

For all the years I enjoyed flowers on my cacti, I never thought about what those flowers can tell us as indicators of overall plant health. Then when I read Elton's article on supplementing ferts with Ammonium sulfate, he clearly states that Ammonium as the primary source of Nitrogen for cacti leads to increased flower production. Simply put, healthier cacti produce more flowers, and I can attest to what Elton says from my own experience -- since I started supplementing my Dyna-Gro with Ammonium sulfate, I've seen cacti flower this year when they didn't last year, while other cacti are blooming earlier and more often than they did before.

Here's an example of 1 cactus in my collection that bloomed for the first time this year. May not seem impressive at first, but I think you'll find the story rather interesting. When I was looking around for cacti that would start the new collection in 2011, I couldn't resist a Sulcorebutia rauschii. What an attractive plant with pretty green-apple skin! That's what it looked like by the end of summer:

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The Sulco went through the same long, dry winter as the Astro (and the rest of my cacti). But the winter and my bad cultivation turned that poor rauschii into...

Sulcorebutia_rauschii04022012.JPG (82.57 KiB) Viewed 3937 times

...Jabba the Hut. In spite of my best efforts with improved cultivation, I got used to the fact that Jabba wouldn't turn back into a rauschii one can recognize. At least the plant is still alive. I was hoping for some kind of progress, and it came as a pleasant surprise to see the beginning of a few new flower buds at the end of May:

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Then the buds went nowhere. By July 1 I figured they would abort (not unexpected, as Sulcos typically flower in spring anyway). But 1 of those buds decided to proceed!

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Please note the appearance of a spiny new little pup next to the bud. (So that's what rauschii pups look like -- nice!) 5 days later the bud was about to pop:

Sulcorebutia_rauschii07242012.JPG (177.37 KiB) Viewed 3937 times

I didn't think the bud would take off that fast. And there's another new pup on the lower right. Now it's showtime:

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Considering what I put the Sulco through, I'm glad to see it healthy enough to keep going. As to the effectiveness of Elton's fert/Ammonium sulfate regimen, I'm convinced, and I hope to offer more success stories. If you have some of your own, post 'em here!

osac wrote:I'am going to pet store to buy PH test and try to get my water to PH 5.5 and also going to buy cacti fertilizer.

Distilled water + cacti fertilizer + lemon juice = would that be ok if I get it to PH 5.5.

What do you think?

Where do I get Ammonium sulfate?

thank you,osac

Well, lemon juice is basically citric acid, so that should do the job. Unfortunately I can't tell you how much you'd need to bring the pH in your water down to the 5.0-5.5 range. Best thing to do is start by measuring out a small amount of lemon juice as you test the pH of your water. Then keep doing it until you reach the desired pH. Once you determine the proper ratio of lemon juice to your water/fertilizer solution, take note of how much lemon juice you used, and that'll tell you how much you'll need every time you water your cacti.

Ammonium sulfate is sold as a fertilizer here in the US, so hopefully it'll be likewise at one of your general-purpose plant nurseries. If not, you'll have to find it online. I get my Ammonium sulfate from Amazon.com, although I can't imagine that you'd want to go through the time and expense of shipping it from overseas. Should you have any trouble buying it locally (or at least in Europe), here's a source in the UK that might be useful:

Any decent gardening supply store should have ammonium sulphate. It is a staple fertiliser ingredient, particular lawn fertiliser since it is high in nitrogen. I don't know how things are organised in Croatia, but here it is sold in regular garden centres. I get mine in plain plastic bags from a general garden supply store, because it is a quarter the price of commercial fertilisers for basically the same thing. About 1 euro per kilo wholesale.

osac wrote:I'am going to pet store to buy PH test and try to get my water to PH 5.5 and also going to buy cacti fertilizer.

Distilled water + cacti fertilizer + lemon juice = would that be ok if I get it to PH 5.5.

What do you think?

Where do I get Ammonium sulfate?

thank you,osac

Lemon juice contains sugars, which could encourage fungal activity in the soil, particularly in a rich soil mix. I'd try and use a different acid, if possible. The best to use would be Nitric or Sulphuric acid, but they're only questionably safe in hobbyist's hands and they might also be difficult to get a hold of. Stick to white vinegar as your acid is my advice on this matter.

CactusFanDan wrote:Lemon juice contains sugars, which could encourage fungal activity in the soil, particularly in a rich soil mix. I'd try and use a different acid, if possible. The best to use would be Nitric or Sulphuric acid, but they're only questionably safe in hobbyist's hands and they might also be difficult to get a hold of. Stick to white vinegar as your acid is my advice on this matter.

Sorry -- didn't think about that. I use 5% white vinegar -- easily available at any grocery store, and perfectly safe for hobbyists. Same goes for straight citric acid (not lemon juice!), although I don't know if there would be any advantage to it over vinegar. Nitric and Sulfuric acids need to be handled very carefully, so unless you have a large collection or plan on opening up a nursery, go with the safe stuff.

Any concentrated acid is dangerous. Concentrated (or glacial) acetic acid is highly corrosive and just the fumes will damage your lungs. Glacial acetic acid is fairly widely available although you won't run across it by accident. Mineral acids tend to be found more often in concentrated form and less often in dilute form because there is little use for the diluted forms. So people have developed the idea that they are "dangerous" while acids such as acetic and citric are "safe".

Citric acid is actually stronger than acetic acid, also triprotic, but it is less commonly available in concentrated form. Citric acid is useful for making buffers because of the dissociation constants of its second and third protons. In the diluted forms you're likely to find, both acetic acid and citric acid are safe, edible even There is some speculation that the acetates produced after neutralisation of hard water by acetic acid can be helpful in transport of nutrients into plants. Citric acid would presumably do the same, it is widely used as a chelating agent in cleaning, although I haven't seen anything written about it relating to plants. The two are closely linked chemically and both citrates and acetates occur in natural (animal) metabolic cycles that also involve lactic acid.

I have been to pet store and bought SERA PH test used in aquaristic , also I have bought Cacti fert. from COMPO 6+5+11 NPK with micro elements.I was thinking lemon juice in first place because it was safe acid but now I think will try with vinegar.

Have to find ammonium sulphate , but will go without it for now. I know that fish in aquarium secrete amonium and that plants love that but not sure that it is ammonium sulphate but it could be. So when I get aquarium will use that water instead of distilled maybe.

Except that ... it's winter and not sure about using fertilizer now, maybe just once as I did not use it at all and than just watering without fert. during winter.